We have attempted to develop the methodology which will allow the transfer of cloned genes into hemopoietic stem cells. Hemopoietic stem cells were chosen because (A) these cells are multipotential, (B) can be cultured in vitro permitting analysis of individual progeny, and (C) will reconstitute the hemopoietic compartment of a lethally irradiated mouse. This latter propery makes feasible the study of long-term regulation in vivo and in vitro and also opens new possibilities for genetic therapy of such hemopoietic diseases as sickle cell anemia and thalassemia. We have approached these experiments from two directions. First, we have gained substantial experience with making viral constructs containing genes of interest and appropriate regulatory sequences. We have now completed work which demonstrates that constructions containing the EJ bladder carcinoma gene will infect and transform erythroid progenitors in a manner that provides a growth advantage without blocking differentiation. As the erythroid cells mature and synthesize hemoglobin and other red cell proteins, they also synthesize copious amounts of the oncogene protein p21. Second, we have used similar constructs to demonstrate for the first time that multipotent hemopoietic stem cells can be directly infected and that their differentiated progeny will express the transferred genetic information.